Effect of Exhaust Gas Recirculation on Combustion Characteristics of Ultra-Low-Sulfur Diesel in Conventional and PPCI Regimes for a High-Compression-Ratio Engine

Low temperature combustion (LTC) mitigates the nitrogen oxide (NOx) and particulate matter (PM) trade-off in conventional compression ignition engines. Significant research on LTC using partially premixed charge compression ignition (PPCI) has typically reduced the compression ratio of the engine to control combustion phasing and lower peak temperatures. This study investigates LTC using PPCI with a high-compression-ratio (=21.2) engine by varying fuel injection timing (FIT) from 12.5° to 30.0° before top dead center (BTDC) while modulating EGR (0%, 7%, 14%, and 25%). Advancing FIT led to a gradual rise in the equivalence ratio of the mixture, in-cylinder pressure, temperature, and rate of heat release due to energy losses associated with ignition occurring before the end of the compression stroke. PPCI was successfully achieved with minimal performance impact using a combination of FIT advancements in the presence of high rates of EGR. Specifically, fuel injected at 25.0° BTDC and 25% EGR reduced PM emissions by 59% and total hydrocarbons by 25% compared with conventional FIT (12.5°) without EGR. Moreover, carbon monoxide and NOx emissions were comparable across set points. As a result, PPCI using high compression ratios is possible and can lead to greater thermal efficiencies while reducing emissions.